Background: Bacteria usually secrete a variety of extracellular enzymes to degrade extracellular macromolecules to meet their nutritional needs and enhance their environmental adaptability. Bacillus cereus 0–9, a biocontrol bacterial strain isolated from wheat roots, has three genes annotated as encoding amylases in the genome, but their functions are unknown, and whether they are involved in the colonization process of the bacterium remains to be further studied. Methods: Mutant gene strains and fluorescently tagged strains were constructed by homologous recombination, and amylase protein was expressed in the prokaryotic Escherichia coli BL21(DE3) expression system. The iodine staining method was used to measure the activity of amylase proteins. We further observed the colonization abilities of the test strains in wheat roots through frozen section technology. Results: The results showed that there were three amylase-encoding genes, amyC, amyP and amyS, in the B. cereus 0–9 genome. Among the three amylase encoding genes, only amyS produced extracellular amylase whose secretion was related to signal peptide at position 1–27. The AmyS protein encoded by the amyS gene is an α-amylase. The growth of Rhizoctonia cerealis was inhibited 84.7% by B. cereus 0–9, but the biocontrol ability of the ΔamyS strain decreased to 43.8% and that of ΔamyS/amyS was restored when the amyS gene was complemented. Furthermore, the biocontrol ability of the ΔamySec strain was decreased to 46.8%, almost the same as that of the ΔamyS mutant. Due to the deletion of the amyS gene, the colonization capacities of ΔamyS (RFP) and ΔamySec (RFP) in wheat roots decreased, while that of ΔamyS/amyS (RFP) was restored after the amyS gene was complemented, indicating that the amyS gene influences the colonization of B. cereus 0–9 in wheat roots. In addition, the colonization and biocontrol abilities of the mutant were restored after the addition of sugars, such as glucose and maltose. Conclusions: B. cereus 0–9 encodes three genes annotated as amylases, amyC, amyP and amyS. Only the deletion of the amyS gene with a signal peptide did not produce extracellular amylase. The AmyS protein encoded by the amyS gene is an α-amylase. Our results indicated that the amyS gene is closely related to the colonization abilities of B. cereus 0–9 in wheat roots and the biocontrol abilities of B. cereus 0–9 to fight against R. cerealis. The extracellular amylase produced by B. cereus 0–9 can hydrolyze starch and use glucose, maltose and other nutrients to meet the needs of bacterial growth. Therefore, it is very possible that the secretion and hydrolytic activities of extracellular amylase can promote the colonization of B. cereus 0–9 in wheat roots and play important roles in the prevention and control of plant diseases. Our results contribute to exploring the mechanisms of microbial colonization in plant roots.

Anthracnose caused by Colletotrichum graminicola (Ces.) G.W.Wils is a significant disease of maize (Zea mays) worldwide. To obtain an efficient biocontrol strain and elucidate its mechanisms, 103 bacterial isolates were obtained from soil samples collected in the Tianshan Mountains, Xinjiang, China. Among these, Bacillus atrophaeus F4’s fermentation broth had the highest efficacy in controlling maize anthracnose, reaching 79.78%. To further investigate biocontrol mechanisms of F4 strain, its complete genome was sequenced, assembled, and annotated. Lipopeptides extracted from the fermentation broth of F4 were found to strongly inhibit the growth of hyphae and the germination of conidia in the pathogen. Microscopic and biochemical analyses indicated that the lipopeptide extract inhibited chitin synthesis and disrupted the integrity of the cell wall and membrane, thereby exerting antifungal effects. Further MALDI-TOF MS analysis identified antimicrobial compounds, including surfactin, iturin, and fengycin B, in the lipopeptide extract. Furthermore, plate antagonistic test showed that F4 strain exhibited broad-spectrum antagonistic activity against multiple plant pathogenic fungi. F4 strain also displayed motility, biofilm-forming capacity, and the ability to produce extracellular enzymes such as proteases and amylases, which are associated with biocontrol activity. These findings suggest the significant potential of B. atrophaeus F4 as a biocontrol agent against maize anthracnose.